economist.) The study of the problem 'what are the conditions which must
be satisfied whenever anything at all is known' is precisely what Kant
meant by _Criticism_, though the raising of the problem in this
definite form is not due to Kant but goes back to Plato, who made it the
subject of one of his greatest dialogues, the _Theaetetus_. The simplest
way to make the nature and importance of the problem clear is perhaps
the way Mr. Russell adopts in the _Problems of Philosophy_--to give a
very rough statement of Kant's famous solution.

Kant held that careful analysis shows us that any piece of knowledge has
two constituents of very diverse origin. It has a _matter_ or material
constituent consisting, as Kant held, of certain crude data supplied by
sensation, colours, tones of varying pitch and loudness, odours,
savours, and the like. It has also a _form_ or formal constituent. Our
data, when we know anything at all, are arranged on some definite
principle of order. When we recognize an object by the eye or a tune by
the ear, we do not apprehend simply so much colour or sound, but colours
spread out and forming a pattern or notes following one another in a
fixed order. (If you reverse the movement of a gramophone, you get the
same notes as before, but you do not get the same tune.) Further, Kant
thought it could be shown that the data of our knowledge are a
disorderly medley and come to us from without, being supplied by things
which exist and are what they are equally whether any one perceives them
or not, but the element of form, pattern, or order is put into them by
our own minds in the act of knowing them. Our minds are so constructed
that we _can_ only perceive things or think of them as connected by
certain definite principles of orderly arrangement. This, he thought,
explains the indubitable fact that we can sometimes know universal
propositions to be true without needing to examine all the individual
instances. I can know for certain that in every triangle the greater